This application claims the priority of Korean Patent Application No. 2003-78041, filed on Nov. 5, 2003, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.
1. Field of the Invention
The present invention relates to a fluid dynamic bearing motor, and more particularly, to a fluid dynamic bearing motor which can improve a load support force of a fluid dynamic bearing and effectively prevent leakage of oil.
2. Description of the Related Art
A fluid dynamic bearing motor typically has an oil gap formed between a rotor and a stator of the motor. The oil gap is filled with oil having a predetermined viscosity and the oil is compressed as the rotor rotates so that fluid dynamic pressure is generated to rotatably support the rotor. Also, to increase the fluid dynamic pressure, an oil groove is formed in surfaces of the rotor and the stator forming the oil gap and facing each other.
FIGS. 1 and 2 show an example of the fluid dynamic bearing motor. Referring to FIGS. 1 and 2, the fluid dynamic bearing motor that is of a shaft rotating type includes a stator constituted by a housing 10, a sleeve 20, and a core 30, and a rotor constituted by a shaft 40, a hub 50, and a magnet 60.
The sleeve 20 has a hollow at a center thereof in which the shaft 40 is inserted to be capable of rotating. An oil groove 22 for generating fluid dynamic pressure is formed in an inner circumferential surface 21 of the sleeve 20. In particular, a thrust 70 having a ring type disc shape is provided at an inner circumferential portion of a lower end of the sleeve 20, corresponding to a lower end portion of the shaft 40, capable of rotating with the shaft 40. The core 30 around which a coil is wound is fixed at a center portion inside the housing 10. A groove (not shown) for generating the fluid dynamic pressure is formed in upper and lower surfaces of the thrust 70 so that the fluid dynamic pressure is generated in an axial direction.
The lower end portion of the sleeve 20 is blocked from the outside as the inner circumferential portion is shielded by a cover plate 80. The thrust 70 contacts the upper side of the cover plate 80 to be capable of rotating. The hub 50 is integrally coupled to the upper end of the shaft 40 which is inserted in the inner circumferential portion of the sleeve 20 capable of pivoting. The hub 50 has a shape of a cap having an open bottom side. The magnet 60 is installed on an inner circumferential surface of an extended end portion of the hub 50, to face an outer circumferential surface of the core 30.
In the above configuration, a fine oil gap is formed between the inner circumferential surface of the sleeve 20 and each of the shaft 40 and the thrust 70. The oil gap is filled with oil having a predetermined viscosity. As the oil in the oil gap converges into the oil groove 22 of the sleeve 20 and the groove of the thrust 70 for generating the fluid dynamic pressure, when the shaft 40 rotates, the oil gap is always maintained uniformly so that the shaft 40 can be stably driven.
In the conventional shaft rotating type fluid dynamic bearing motor configured as above, when external power is applied to the core 30, the hub 50 having the magnet 60 attached thereto rotates by an electromagnetic force generated between the core 30 and the magnet 60. Accordingly, the shaft 40 coupled to the hub 50 rotates at the same time.
During operation of the motor, the shaft 40 inserted in the inner circumferential portion of the sleeve 20 can smoothly rotate without contacting the inner circumferential surface of the sleeve 20 by the fluid dynamic pressure generated between the oil groove 22 formed in the inner circumferential surface 21 of the sleeve 20 and a groove (not shown) formed in an outer circumferential surface of the shaft 40.
However, the conventional fluid dynamic bearing motor configured as above has the following drawbacks.
First, the oil groove 22 of the fluid dynamic bearing simultaneously performs functions of supporting a load of the rotor and preventing leakage of the oil, by increasing the pressure of the oil during the rotation of the rotor. To increase the load support force, it is advantageous to increase an angle A of the oil groove 22 in view of the dynamics. In contrast, to prevent leakage of the oil, it is advantageous to decrease the angle A. However, since the oil groove 22 is typically formed at a predetermined angle, the improvement of the load support force and the prevention of leakage of the oil cannot be performed simultaneously and effectively.
Second, as shown in FIG. 2, since the direction of flow of the oil in the oil gap and an end portion 22a of the oil groove 22 is parallel to the direction of rotation of the shaft 40, an area whose pressure (negative pressure) is less than the atmospheric pressure is formed narrow in the end portion area of the oil groove 22. As a result, the oil leaks due to high internal pressure in the oil gap.